Method for producing a coking additive by delayed coking

ABSTRACT

This invention relates to the field of oil refining and, in particular, to a delayed coking process that produces coke with a volatile substances content of 15-25% for use as a coking additive in a coal coking charge in the production of metallurgical coke. The invention is directed towards increasing the content of volatile substances in coke and increasing the efficiency of a plant. The method comprises preheating a primary raw material, mixing the latter with recycle in a tank in order to form a secondary raw material, heating the secondary raw material to 455-470° C. and supplying the latter to a coking chamber, and coking to form a coking additive. It is expedient to feed an antifoaming additive into the coking chamber 3-5 hours before coking is finished. It is preferable to feed in the antifoaming addition agent at two-four points around the perimeter of the coking chamber.

This invention relates to oil refining, in particular to delayed cokingthat produces coke containing 15-25% of volatiles substances, which canbe used as a coking additive in a coal coking charge for metallurgicalcoke production.

Oil coke with more than 14% but less than 25% volatiles is capable notonly of replacing the K-brand (coking) coal, which is in short supply,in coal coking charges, but also of improving the quality ofmetallurgical coke (Russian Federation Patent 2355729, C10B57/04,published on 20 May 2009).

There exists technology for forming oil coke by delayed coking of oilresidues. This method includes slowly heating raw materials to 490-515°C. in a tubular furnace, mixing the raw materials with a recirculant,presenting the coking distillate products formed inside the cokingchamber, in a rectification column, which produces bottoms, supplyingthe bottoms as the secondary raw materials to the coking chamber at485-495° C. and carrying out coking, which results in the formation ofcoke (Z. I. Syunyaev, “Forming, Refining and Using Petroleum Coke”,Moscow: Khimiya: 1973, p. 95).

The drawback of this method is that the coke formed by its applicationhas a high strength and low concentration of volatiles (up to 9% bymass).

It is possible to increase the concentration of volatiles in coke byreducing the temperature of the raw materials at the inlet into thecoking chamber. However, reducing that temperature and coking at lowtemperatures results in excessive foaming and, consequently, itincreases the probability of the foam getting into the rectificationcolumn, then into the furnace, which might result in the plant becomingcoked up, shortening the spans between overhauls.

A delayed coking method, capable of guaranteeing that no direct contactwould occur between the primary charge and the vapours reaching therectification column from the coking chamber during the formation of thesecondary charge, can prevent coke foam finding its way inside thereaction spiral tubes of the furnace, the coking up of the plant andthus lengthen the spans between overhauls.

The technology nearest to the proposed invention is the delayed cokingof oil residues, which includes heating the original raw materials to340-380° C., mixing them with a recirculant—heavy coking gasoil(pyrolisis resin, heavy catalytic cracking gasoil)—in a mixing tankwhere the secondary charge forms, heating the secondary charge, i.e. theheavy residues formed in the mixing tank, transferring this into thecoking chamber at 485-505° C., and coking to form coke (RussianFederation Patent No. 2206595, class C10B 55/00, published on 20 Jun.2003).

The drawback of this invention is the low concentration of volatiles inthe final product due to the high coking temperature (485-505° C.) andthe low efficiency due to extensive foaming, and consequently to notbeing able to use the coking chamber to its full capacity.

This invention aims at increasing the concentration of volatiles in thecoke and improving the efficiency of the plant.

This aim is achieved because this method of delayed coking of a cokingadditive includes preheating of the primary raw materials at 270-350°C., mixing the primary raw materials with the recirculant in the tankfor the production of secondary charge, heating the secondary charge,transporting it to the coking chamber, and coking to form the targetproduct. In this invention the secondary charge is heated at 455-470° C.before it reaches the coking chamber.

Moreover, to prevent foaming, an anti-foaming dope is introduced intothe coking chamber 3-5 hours before the end of coking.

Moreover, taking into consideration that the foam developed inlow-temperature coking forms a thick layer, the anti-foaming dope isintroduced in two to four areas around the perimeter of the cokingchamber, so that it covers the entire surface of the foam.

Coking carried out at low temperatures, because the raw material ischarged into the coking chamber at a low temperature, produces coke witha concentration of volatiles of 15-25% to be used as a coking additive.

Introducing the anti-foaming dope during the last 3-5 hours of thecoking process not only reduces the amount of foam forming in the cokingchamber but also makes the process more efficient with respect to theprimary raw materials.

The diagram shows the main parts of the plant for carrying out theproposed method for production of a coking additive by the means ofdelayed coking.

The proposed method of production of a coking additive in delayed cokingworks as follows.

The original raw materials, such as tar, de-asphalting asphalt, oilproduction extracts, heavy gasoil of catalytic cracking or any mixturesof the above, are heated in a tubular furnace 1 to 270-350° C., thendischarged into the mixing tank 2 connected in pairs to therectification column 3. Heavy coking gasoil, used as the recirculant, isalso charged into the rectification column 3. It is discharged fromcolumn 3 as a side fraction.

The mixture of the primary raw materials and recirculant, which becomesthe secondary charge, is heated to 455-470° C. in the tubular furnace 4,then fed into the alternately working coking chambers 5 where a cokingadditive with 15-25% volatiles is gradually accumulated. The distillatecoking products, formed in the coking chamber 5, are discharged into therectification column 3, where they are resolved into a gas, benzene,light and heavy coking gasoil and the bottoms.

Vapour-like products leave the plant through the top of the column 3,light and heavy gasoils are discharged from the middle part of thecolumn, while the bottoms are removed from the bottom part. To reducefoam formation, the anti-foaming dope 6 is introduced in four areasaround the perimeter of the coking chamber.

The suggested technology is illustrated with the following fourexamples: 1-4.

A mixture of raw materials, comprised of a vacuum visbreaking residue,tar oil and heavy gasoil of catalytic cracking in the ratio of 15:75:10was coked, using an industrial delayed coking plant. The mixture had thefollowing characteristics: density 1.055 g/cm³, cokeability 25.8% andsulphur content 3.8%. The primary charge was heated in a convectionfurnace to 320° C., then it was mixed with a recirculate: heavy cokinggasoil, discharged from the rectification column as a side fraction. Theproduced secondary charge was heated in a tubular furnace, then it wasfed into the coking chamber to produce a coking additive. When cokingwas over, the coke was steamed out, water-cooled and discharged byhydraulic means. In Examples 2 and 4, an anti-foaming dope wasintroduced into the coking chamber 4 hours before the end of theprocess—to prevent foam formation.

Coking conditions and results in Examples 1-4 are shown in the Table.

For comparison, the same charge as in 1-4 was coked, using thetechnology of the prototype of this invention. The temperature of thesecondary charge at the inlet of the coking chamber was 485° C. Noanti-foaming dope was used. The result was ordinary electrode coke witha concentration of volatiles of 10.8%. The conditions and results arealso presented in the Table.

TABLE Comparative Data on Coking of Raw Materials Example Inventiontechnology Prototype Characteristics 1 2 3 4 5 Plant efficiency 96 10096 98 95 with respect to primary charge, m³/h Plant efficiency 106 110110 112 105 respective the secondary charge, m³/h Secondary charge 468468 456 456 485 temperature at the coking chamber inlet, ° C. Cokingduration, h 16 16 16 16 16 Coke level in the 19.0 20.5 19.5 21.0 19.0chamber, m Concentration of 15.1 15.5 21.8 22.4 10.8 volatiles in coke,% Anti-foaming dope, No Yes No Yes No yes/no

As can be seen from the Table, the coking method suggested by thisinventor produces coke that can be used as a coking additive, with aconcentration of volatiles higher than 15%. Introducing it into thecoking chamber at 456° C. is not practicable because bitumen is likelyto form, and it would make the steaming out and cooling down of cokedifficult. On the other hand, a charge introduced at a temperature above470° C., will produce coke that contains less than 15% of volatiles.

Introduction of the anti-foam dope into the top part of the cokingchamber reduces the amount of foam that forms during coking, whichimproves the working efficiency of this technology with respect to theoriginal raw material.

1-3. (canceled)
 4. A method of producing a coking additive in delayedcoking, comprising: heating a primary charge to 270-330° C.; mixing theprimary charge with a recirculate in a tank to form a secondary charge;heating the secondary charge and introducing it into a coking chamber;and coking to form a target product; wherein the secondary charge isintroduced into the coking chamber at 455-470° C.
 5. The methodaccording to claim 4, further comprising introducing an anti-foamingdope into the coke chamber 3-5 hours before the end of coking.
 6. Themethod according to claim 5, wherein the anti-foaming dope is introducedinto 2-4 areas around a perimeter of the coking chamber.